Hoses for use in systems operating at high temperatures or high pressures and/or in high vibrational environments must possess certain characteristics for satisfactory performance in such environments, thereby precluding premature failure of the hoses due to the severe operating conditions. For example, it has been found that the performance of turbocharged internal combustion engines may be enhanced through the use of charge air cooling systems.
Charge air cooling systems provide cooler, denser air to the engine to achieve more complete combustion. Increased combustion efficiency improves fuel economy by 2-10 percent over conventional cooling methods, lowers engine emission levels and greatly increases engine component reliability.
In charge air cooling systems, ambient air is compressed in the turbocharger and directed through ducting to a heat exchanger. The heat exchanger utilizes ram air generated by vehicle movement to cool the charge air which is then directed through ducting to the engine via a bypass blower.
The charge air from the turbocharger has a temperature in excess of 300.degree. F. and is ram cooled to a temperature in the range of 110.degree. F. The cooled charge air is extremely dense air. Thus, it is readily apparent that hose utilized in ducting such systems must be capable of maintaining mechanical strength and integrity under high temperatures and pressures.
In charge air systems as described above, the turbocharger and heat exchanger are mounted on different portions of the system, each of which is subjected to different three-dimensional vibrations. Thus, hose utilized as ducting in such systems must also possess a certain degree of flexibility to preclude the hose from being subjected to fatigable strain due to three-dimensional vibrations in disparate planes.
Such flexibility in the hose, however, should be limited to compensating for the strain effects resulting from high temperatures and pressure and three-dimensional vibrations without adversely degrading the structural strength and integrity of the hose. Generally this requires that such hose should be capable of a predetermined degree of flexibility along the longitudinal axis of the hose while being substantially impervious to radial expansion and contraction to preclude ballooning or collapse of the hose during start up, irregular or steady state operation of the system.
In addition to the severe operating environments encountered in turbocharged truck, bus, automobile, marine and stationary engines as exemplarily described hereinabove, it will be appreciated that similar severe conditions exist in other hose applications.
It is known in the art to utilize hoses fabricated from metal in systems operating at high temperatures and/or high pressures and/or subjected to severe vibrational stresses. While metallic hoses possess good mechanical strength and integrity, such hoses must be fabricated to a high degree of precision to prevent misalignments, making such hoses relatively costly. In addition, metallic hoses can be disadvantageous in high vibrational environments. While the hoses themselves may or may not experience debilitating vibrational stresses, the hoses will transmit vibrational stresses to adjacent system components.
It is also known in the art to provide shaped hoses formed from natural or synthetic rubbers for use in such severe operating environments. Shaped hoses include one or more convoluted sections to provide the requisite degree of flexibility in the hose. However, even though shaped hoses are fabricated as integral units, structural discontinuities exist at the interfaces between the convoluted sections and the tubular sections of the hose. The stresses experienced by shaped hoses are concentrated at these discontinuities which increases the probability of premature failure at these points. To provide improved reliability and longevity, shaped hoses may be fabricated with wall dimensions larger than required for the operating conditions, but at the expense of increased costs and decreased flexibility.
It is also known in the art to use reinforcing elements in hoses formed of natural or synthetic rubbers to improve the durability, reliability and longevity thereof. Reinforcing elements may include filaments of natural or synthetic fibers or metal, natural or synthetic fabrics and metallic mesh.
Filaments of natural or synthetic fibers or metal may be wound between layers of natural or synthetic rubber to provide a hose with increased mechanical strength. The filament windings restrict the radial flexibility of the hose. These windings, however, are generally ineffective in controlling the longitudinal flexibility of the hose. Furthermore, filaments of natural or synthetic fibers such as cotton, wool, nylon, polyester and dacron are adversely affected by high temperature environments.
Filaments formed from materials such as fiberglass have a tendency to fragment in high vibrational environments. Fiberglass fragments will lacerate adjoining rubber layers, leading to premature hose failure. Metallic filaments likewise have a tendency to lacerate adjoining rubber layers. Lacerating effects may be mitigated by encasing such filaments between fabric layers. However, such hoses require additional costs and time to fabricate and may result in hoses of unnecessarily large dimension and weight.
Filaments of natural or synthetic fibers may be woven as fabrics which are then utilized as laminations between layers of natural or synthetic rubber. Fabrics woven from filaments of natural or synthetic fibers such as cotton, wool, nylon, polyester and dacron are adversely affected by high temperature environments.
Moreover, as illustrated in U.S. Pat. Nos. 4,600,615 and 4,576,205, the warps and wefts of the woven fabric are generally orientated longitudinally and radially perpendicular to the axis of the hose which presents difficulty in achieving the requisite horizontal flexibility in combination with restricted radial flexibility. A proper balance in flexibility may be achieved by utilizing different filament yarns in warp and weft, by coiling right-handed and/or left-handed fiber yarn about the warp and weft fibers and/or coiling crimped yarns about the warp and/or weft fibers. This, however, increases the complexity and cost of the woven fabric as well as resulting in a hose of increased weight.
Metallic mesh may be utilized as a reinforcing layer between layers of natural or synthetic rubber to provide hoses of high mechanical strength. Metallic mesh, however, severely restricts the flexibility of the hose both longitudinally and radially. In addition, metallic mesh likewise has a tendency to lacerate adjoining rubber layers. Lacerating effects may be mitigated by encasing such mesh between fabric layers. However, such hoses require additional costs and time to fabricate and may result in hoses of unnecessarily large dimension and weight.